So you have just installed Centos 6 and for some reason, although you can SSH into the server, you can’t SSH into another server.

ssh: command not found

You check that you have openssh installed by running yum intall openssh and find that it’s already installed. What has happened here then? Although you have the openssh server installed and running (as you are connected over ssh), you don’t have an ssh client installed. So run:

yum install openssh-clients

This will install an openssh client and you can now connect to other servers via SSH etc.